package 栈和队列;

import java.util.Stack;

/**
 * ---------------------------------------------------------
 * <h></h>
 * <p>
 * 用两个栈实现一个队列。队列的声明如下，请实现它的两个函数 appendTail 和 deleteHead ，分别完成在队列尾部插入整数和在队列头部删除整数的功能。(若队列中没有元素，deleteHead 操作返回 -1 )
 *
 *  
 *
 * 示例 1：
 *
 * 输入：
 * ["CQueue","appendTail","deleteHead","deleteHead"]
 * [[],[3],[],[]]
 * 输出：[null,null,3,-1]
 * 示例 2：
 *
 * 输入：
 * ["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
 * [[],[],[5],[2],[],[]]
 * 输出：[null,-1,null,null,5,2]
 * 提示：
 *
 * 1 <= values <= 10000
 * 最多会对 appendTail、deleteHead 进行 10000 次调用
 *
 * 链接：https://leetcode-cn.com/problems/yong-liang-ge-zhan-shi-xian-dui-lie-lcof
 * </p>
 * Created by Frank on 2021/4/2.
 * <a href="mailto:frankyao10110@gmail.com">Contact me</a>
 * ---------------------------------------------------------
 */
public class _两个栈队列头删尾增 {
    public class CQueue {

        Stack<Integer> inStack;
        Stack<Integer> outStack;

        public CQueue() {
            inStack = new Stack<>();
            outStack = new Stack<>();
        }

        public void appendTail(int value) {
            inStack.push(value);
        }

        public int deleteHead() {
            if (outStack.isEmpty()) {
                while (!inStack.isEmpty()) {
                    outStack.push(inStack.pop());
                }
            }

            //outStack不为空
            if (outStack.isEmpty()) {
                return -1;
            }else {
                return outStack.pop();
            }
        }
    }
}
